The hummocks of Mount St. Helens' northern slope look decidedly haphazard. Barren, knuckle-shaped hills alternate with groves of red alder. A straggly willow grows from a mound of rocky soil. Patches of yellow moss are broken by wild strawberry blossoms and the occasional flare of red paintbrush. The effect is unsettling, as if the landscape were the result of a giant habitat-components lottery.

Seated on the banks of a small pond in mid-May, ecologist Charlie Crisafulli stuffs a frog into a sandwich bag. "Trap three," Crisafulli says to a field assistant taking notes. He holds a ruler to the animal and gently pinches it so its limbs splay out. "Length of 152 (millimeters), and snout, vent, 74 (millimeters). We have a bulbous male."

Crisafulli releases the frog into the murky water with a plop. Twenty-four hours ago, his team planted funnel traps in six different ponds; now, they're cataloguing the captured amphibians.

In the 31 years since a volcanic eruption obliterated the mountain's forests and showered its lakes with burning debris, amphibians have returned with astounding speed. The Western toad and Pacific treefrog led the way, and by 1990, all the pond-dwelling amphibians that typically inhabit southern Washington's Cascade Range were somewhere on the volcano. Part of that abundance is due to the post-eruption environment: It's taken longer for predators to return, and there's less competition for habitat. It also helps that the hummocks region lies within the Mount St. Helens National Volcanic Monument, a 110,000-acre area around the summit where the landscape has been left mostly untouched. It's essentially a living laboratory of how an ecosystem recovers without human tinkering.

That's the theory, anyway. But the monument has never truly stood in isolation; its borders are dotted with timber farms and its rivers flow past a fish hatchery and several towns. As a result, human-influenced changes have sometimes clashed -- and blended -- with the mountain's "natural" recovery. A push here, a snip there, and what has emerged is a landscape of surprises, one that blurs the line between expected regrowth, deliberate engineering and random chance.

In 1979, St. Helens was postcard-perfect, a snow-capped cone rising 9,700 feet above southern Washington. Over 500,000 people visited that year to hike, hunt, camp and fish. Farther downslope, the mountain hosted a thriving timber industry.

The earthquakes began in March of 1980. For two months they rocked the mountain, as magma pushed its northern slope outward. Then, on May 18, that slope collapsed in the biggest landslide in recorded history. A mixture of steam, rocks and hot gas exploded sideways from the crater, charging down the mountainside and prompting huge mudflows as it melted ice and snow.

The mountain's lush, coniferous forests were flattened. Fifty-seven people died, and nearby communities feared further damage from subsequent landslides. Many thought it would be decades before the mountain resembled its former self. But the volcano was also a scientific gold mine, and in 1982, Congress passed the National Volcanic Monument Act. Everything within the new monument -- which encompassed some of the worst-hit federal, state and private lands -- became Forest Service land, necessitating complex land swaps. Although the monument is open to the public, mining and tree harvesting were banned within its borders, along with off-road motor vehicles. Some 25 percent of the monument received further protection as a research area where visitors are restricted to specific trails. So it was that the monument became a haven for science, education and recreation, allowing "geologic forces and ecological succession to continue substantially unimpeded."

Today, the contrast between the monument and its surroundings is absolute. Thick conifers turn the slopes of bordering Weyerhaeuser lands a uniform dark green; metal signs along the road read Planted 1992; Planted 1986; Planted 2001. Meanwhile, the monument is a checkerboard of habitats, each marking a different stage of ecological recovery: dazzling fields of wildflowers, a barren pumice plain, saplings in the hummocks. For Crisafulli, it's this diversity that makes the monument special: Because of the sheer variety of available niches, it may now be more biologically diverse than before the eruption. That's partly why Crisafulli has worked on the mountain since 1980, first as a graduate student monitoring the return of small mammals, then later as an ecologist with the U.S. Forest Service.